1. Field of the Invention
The present invention relates to laser printers and, more particularly, to a system for conversion of a line density in a laser printer used for a recording section of a facsimile device.
2. Description of the Prior Art
Facsimile terminals using a telephone network are classified into four groups 1-4 according to the Recommendation T.O of CCITT (Consultive Committee in International Telegraphy and Telephony).
The groups 1-3 are purely for using a telephone network while the group 4 is defined for data exchanging purposes and may also be used in a telephone network by using modulation means.
Recently, the group 1 (hereinafter referred to as "G1") terminals tend to decrease in number due to communication expenditure while the terminals belonging to the groups 2, 3 and 4 (hereinafter referred to as "G2", "G3" and "G4", respectively) tend to be predominant.
In recording units used in the recording sections of such facsimile devices, the scanning line density is prescribed in a millimeter system at the G2 and G3 terminals while it is prescribed in an inch system at the G4 terminals, so that conversion between their scanning line densities is required in order to achieve compatibility.
For example, as shown in FIG. 1, conventional conversion of such scanning line density is performed by appropriately demodulating an incoming image signal fed through a telephone network or a data exchange network at a transmission control unit 1, and then converting the scanning line density of the demodulated image signal using a main-scan line density conversion unit 2, a sub-scan line density conversion unit 3 and a memory 4 such that the scanning line density of the demodulated signal meets the standard of a printer 5.
If, for example, image data in a millimeter system (16 dots/mm.times.15.4 lines/mm) is printed by a printer in an inch system (for example, of 400 ppi (pulses per inch) type), the following main-and sub-scanning direction conversions are required: